Impermeable inner shell for a breast implant

ABSTRACT

An implantable device includes a first sealed flexible shell configured for implantation within a breast of a human subject, an elastic filler material contained within the first sealed flexible shell, and a second sealed flexible, inelastic shell, which is disposed within the elastic filler material inside the first sealed flexible shell and is inflated with a volume of gas. The second shell includes a material selected such that an amount of the gas escaping from the second shell does not exceed 10 −8  Torr-liter/second when the gas pressure inside the second shell is 250 mbar higher than the gas pressure outside the second shell.

FIELD OF THE INVENTION

The present invention relates generally to medical devices, andparticularly to breast implants.

BACKGROUND

A breast implant is either inserted in a human breast or attached on thebreast in order to replace tissue that has been medically removed in anoperation such as a mastectomy. The purpose of the breast implant is torestore to the breast its external form, including its tactile feel andweight. A breast implant may also be inserted in a breast to enhance orenlarge the appearance of the breast for cosmetic purposes.

PCT Patent Application WO2015132158 describes a medical implant which isvacuum-packed within an air tight cover material.

U.S. Patent Application 2007/0093911 describes a soft tissue implantsuch as a breast implant, which comprises an external shell-typeenvelope of flexible plastic material, in particular of silicone, aliquid to viscous filler material contained in the envelope, and ametal-containing, biocompatible, continuous coating on the outside ofthe envelope.

PCT Patent Application WO2011058550 describes a breast implantcomprising an envelope and a filling, and wherein the filling comprisesa gaseous phase.

U.S. Patent Application 2009/0099656 describes a breast implant withouter spherical layers, layer of silicone gel and an inner core of gasfilled silicon spheres.

U.S. Patent Application 2012/0277860 describes a prosthetic implantmaterial for use in a prosthetic implant, comprising a gel andoptionally a gas.

U.S. Pat. No. 5,376,117 describes a breast implant including an outershell having a smooth non-porous outer envelope and a non-woven porousouter layer affixed to the envelope.

SUMMARY

Embodiments of the present invention that are described hereinbelowprovide for an improved breast implant.

There is therefore provided, in accordance with an embodiment of thepresent invention, an implantable device, which includes a first sealedflexible shell configured for implantation within a breast of a humansubject, an elastic filler material contained within the first sealedflexible shell, and a second sealed flexible, inelastic shell, which isdisposed within the elastic filler material inside the first sealedflexible shell and is inflated with a volume of a gas. The second shellis constructed of a substance impermeable to the gas, such that anamount of the gas escaping from the second shell does not exceed 10⁻⁸Torr-liter/second when the gas pressure inside the second shell is 250mbar higher than the gas pressure outside the second shell.

In an embodiment the second sealed flexible, inelastic shell includes afirst composite of polyamide and polyurethane, and a second composite ofpolyurethane and ethylene vinyl alcohol.

In another embodiment at least one coating impermeable to the gas isdeposited on the second shell. The coating includes graphene oxide,aluminum oxide, or titanium oxide.

In another embodiment the elastic filler material includes silicone gel.

In a further embodiment the volume of gas includes a volume of air orargon.

There is also provided, in accordance with an embodiment of the presentinvention, an implantable device, which includes a first sealed flexibleshell configured for implantation within a breast of a human subject, anelastic filler material contained within the first sealed flexibleshell, and a second sealed flexible, inelastic shell. The second sealedflexible, inelastic shell is disposed within the elastic filler materialinside the first sealed flexible shell and is inflated with a volume ofa gas, and the second shell includes a first composite layer ofpolyamide and polyurethane overlaying which is cemented to a secondcomposite layer of polyurethane, ethylene vinyl alcohol, andpolyethylene.

There is further provided, in accordance with an embodiment of thepresent invention, an implantable device, which includes a first sealedflexible shell configured for implantation within a breast of a humansubject, an elastic filler material contained within the first sealedflexible shell, and a second sealed flexible, inelastic shell. Thesecond sealed flexible, inelastic shell is disposed within the elasticfiller material inside the first sealed flexible shell and includes atleast one coating including at least one of aluminum oxide, titaniumoxide, and graphene oxide is deposited on the second shell.

There is also provided, in accordance with an embodiment of the presentinvention, a method for manufacturing an implantable device, the methodincluding providing a first sealed flexible shell configured forimplantation within a breast of a human subject, filling the firstsealed flexible shell with an elastic filler material, providing asecond sealed flexible, inelastic shell which is impermeable to a gas,such that an amount of the gas escaping from the second shell does notexceed 10⁻⁸ Torr-liter/second when the gas pressure inside the secondshell is 250 mbar higher than the gas pressure outside the second shell,disposing the second shell within the elastic filler material inside thefirst sealed flexible shell, and inflating the second shell with avolume of the gas.

In an embodiment the second sealed flexible, inelastic shell includes afirst composite of polyamide and polyurethane, and a second composite ofpolyurethane, ethylene vinyl alcohol, and polyethylene.

In a further embodiment providing a second sealed flexible shellimpermeable to a gas includes depositing at least one coatingimpermeable to the gas on the second shell.

In an embodiment the coating includes graphene oxide, and depositing thecoating includes providing graphene oxide as a suspension in a liquid,applying the liquid on an outer surface of the second shell, andallowing the liquid to dry.

In another embodiment the coating includes aluminum oxide, anddepositing the coating includes providing aluminum oxide as a suspensionin a liquid, applying the liquid on an outer surface of the secondshell, and allowing the liquid to dry.

In yet another embodiment the coating includes titanium oxide, anddepositing the coating includes providing titanium oxide as a suspensionin a liquid, applying the liquid on an outer surface of the secondshell, and allowing the liquid to dry.

In an embodiment filling the first sealed flexible shell includesfilling the shell with silicone gel.

In another embodiment inflating the second sealed flexible shellincludes inflating the shell with air or argon.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional illustration of a human female breastwith a breast implant, in accordance with an embodiment of theinvention;

FIG. 2 is a schematic perspective view of a first shell of the breastimplant, in accordance with an embodiment of the invention;

FIG. 3 is a schematic sectional view of PA/PU (polyamide/polyurethane)composite material, in accordance with an embodiment of the invention;

FIG. 4 is a schematic perspective view of cut PA/PU composite materialprepared for RF (radio frequency) welding, in accordance with anembodiment of the invention;

FIG. 5 is a schematic perspective view of a second shell preform afterRF welding of two pieces of PA/PU composite material, in accordance withan embodiment of the invention;

FIG. 6 is a schematic sectional view of a PU/EVOH/PE(polyurethane/ethylene-vinyl-alcohol/polyethylene) composite material,in accordance with an embodiment of the invention;

FIG. 7 is a schematic perspective view of PU/EVOH/PE composite materialafter it has been cut in preparation for cementing to the second shellpreform, in accordance with an embodiment of the invention;

FIG. 8 is a schematic perspective view of the second shell preform aftercementing PU/EVOH/PE composite material sheets onto PA/PU compositematerial and attaching to each other upper and lower sheets by RFwelding, in accordance with an embodiment of the invention;

FIG. 9 is a schematic perspective view of the second shell preform afterthe preform has been inflated with air or other gas, in accordance withan embodiment of the invention;

FIG. 10 is a schematic perspective view of a completed second shellformed from the preform, in accordance with an embodiment of theinvention;

FIG. 11 is a schematic sectional view of PU/EVOH/PE composite materialcemented onto one side of PA/PU composite material, in accordance withan embodiment of the invention;

FIG. 12 is a schematic sectional view of PU/EVOH/PE composite materialcemented onto both sides of PA/PU composite material, in accordance withan alternative embodiment of the invention;

FIG. 13 is a schematic perspective view of a coated second shellpreform, in accordance with an embodiment of the invention;

FIG. 14 is a schematic perspective view of the second shell preformafter the preform has been inflated with air or other gas, in accordancewith an embodiment of the invention;

FIG. 15 is a schematic perspective view of a completed second shellformed from preform, in accordance with an embodiment of the invention;

FIG. 16 is a schematic sectional view of a completed breast implant, inaccordance with an embodiment of the invention; and

FIG. 17 is a flowchart that schematically illustrates a method forfabricating the breast implant, in accordance with embodiments of theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

A commonly used breast implant is an implant wherein an elastic fillermaterial, such as silicone gel, is contained in a first sealed flexibleshell. However, a breast implant that is completely filled with such amaterial is relatively heavy, and may cause discomfort to the wearer ofthe implant.

Embodiments of the present invention provide an implantable device thatis used as a breast implant. The device comprises a first sealedflexible shell that is configured for implantation within a breast of ahuman subject. An elastic filler material is contained within the firstflexible shell.

There is a second sealed, flexible, inelastic shell that is disposedwithin the elastic filler material with a volume of gas within thesecond shell, wherein the second shell is impermeable to the gas.

Embodiments of the present invention that are described herein addressthe potential for gas leakage from the second shell so as to enable theconstruction of a breast implant equipped with a balloon-like secondshell with no appreciable gas leakage over the lifetime of the implant.This enables the construction and fabrication of light-weight and stablebreast implants.

The disclosed embodiments use gas-impermeable composite materials forconstructing the second shell. A material is deemed impermeable to gasif the amount of gas escaping from a closed shell constructed of thematerial typically does not exceed 10⁻⁸ Torr-liter/second for anoverpressure of 250 mbar within the shell. In alternative disclosedembodiments gas-impermeable coatings are deposited on the second shell,with the above definition of gas-impermeability applied to the coatings.The disclosed embodiments reduce any potential gas leakage to ensure ausable life-time of approximately 10 years for a breast implant.

System Description

FIG. 1 is a schematic sectional illustration of a human female breast 20with a breast implant 21, in accordance with an embodiment of thepresent invention. Implant 21 comprises a first shell 22 and a secondshell 23, described in more detail below. In the disclosed embodiment,breast implant 21 is positioned as a subglandular implant between breasttissue 24 and a pectoralis major muscle 26. In alternative embodiments,breast implant 21 may be positioned either as a subfascial, subpectoral,or submuscular implant, referring to different positions of the implantrelative to pectoralis major muscle 26, as will be understood by thoseskilled in the art.

FIG. 2 is a schematic perspective view of first shell 22 of breastimplant 21, in accordance with an embodiment of the invention. Firstshell 22 is fabricated by repeatedly dipping a mandrel (not shown) in asilicone solution. The coat of the silicone solution is allowed tosolidify between consecutive dips. Once a sufficient thickness of thesilicone layer covering the mandrel, typically 0.1 mm, has been reachedand the silicone has solidified, the silicone “skin” is peeled off themandrel. An opening 62 is left in first shell 22 by the stem of themandrel.

FIG. 3 is a schematic sectional view of a PA/PU (polyamide andpolyurethane) composite material 70, in accordance with an embodiment ofthe invention. PA/PU composite material 70, which is a flexible andinelastic, is used for second shell 23. Alternatively, other flexibleand inelastic materials may be used. The flexibility of second shell 23allows the shell to adapt its shape to the changing shape of implant 21due to e.g. movement of breast 20. The inelasticity of second shell 23prevents the shell, and thus implant 21, from changing its size in alow-pressure environment, such as inside an airplane.

Composite material 70 is fabricated by dipping a fine net of PA(polyamide) 72 in a liquid form of PU (polyurethane) 74. The compositeis then fed through two parallel rollers to flatten out the sheet.

FIG. 4 is a schematic perspective view of PA/PU composite material 70after it has been cut in preparation for radio frequency (RF) welding,in accordance with an embodiment of the invention. Two similarly shapedpieces have been cut out of PA/PU composite material 70, forming anupper composite sheet 80 and a lower composite sheet 82 that togetherform a second shell preform 76. As described below sheets 80 and 82 areused to form second shell 23, and the shape of sheets 80 and 82 may becircular, square, or any other desired shape for second shell 23. Anextension 84 is left on each part to form a fill tube 86 (shown in FIG.5) after RF welding.

FIG. 5 is a schematic perspective view of second shell preform 76 afterRF welding of upper and lower composite sheets 80 and 82, respectively,in accordance with an embodiment of the invention. Upper and lowercomposite sheets 80 and 82, respectively, have been RF welded togetheralong a weld line 89 positioned at the perimeters of the sheets. In theprocess, a fill tube 86 has been formed from extensions 84, to be usedfor inflating second shell preform 76.

FIGS. 6-12 show the construction of second shell 23 using a layer ofethylene-vinyl-alcohol, in accordance with an embodiment of theinvention.

FIG. 6 is a schematic sectional view of a composite material 90, inaccordance with an embodiment of the invention. In one embodimentcomposite material 90 comprises a composite of polyurethane andethylene-vinyl-alcohol and polyethylene (PU/EVOH/PE) which is used forcovering PA/PU composite material 70 and thus reducing its permeabilityto gas. PU/EVOH/PE composite material 90 comprises PU layer 74, an EVOHlayer 92, and a PE layer 94.

Alternatively, composite 90 comprises a composite of polyurethane andethylene-vinyl-alcohol (PU/EVOH) and PU/EVOH may be used instead ofPU/EVOH/PE composite to cover PA/PU composite material 70.

FIG. 7 is a schematic perspective view of PU/EVOH/PE composite material90 after it has been cut in preparation for cementing to second shellpreform 76, in accordance with an embodiment of the invention. Twosimilarly shaped sheets 100 and 102 have been cut out of PU/EVOH/PEcomposite material 90. The shapes and sizes of sheets 100 and 102 arechosen to cover second shell preform 76 of FIG. 5, with a sufficientmargin to permit RF welding outside the preform.

FIG. 8 is a schematic perspective view of second shell preform 76 aftercementing sheets 100 and 102 of PU/EVOH/PE composite material 90 ontoPA/PU composite material 70 and attaching to each other upper and lowersheets 100 and 102, respectively, by RF welding, in accordance with anembodiment of the invention. Upper and lower sheets 100 and 102,respectively, have been RF welded together along a weld line 110positioned at the perimeters of the sheets and outside the extent ofsheets 80 and 82 of FIG. 5. Fill tube 86 is still left accessible forinflating second shell preform 76.

FIG. 9 is a schematic perspective view of second shell preform 76 afterthe preform has been inflated with air or other gas, in accordance withan embodiment of the invention. Upper composite sheets 80 together with100 and lower composite sheets 82 together with 102, respectively, haveformed a balloon-like volume due to the inflation of second shellpreform 76 through fill tube 86. Only sheets 100 and 102 are visible inFIG. 9, as sheets 80 and 82 are on the inside of the balloon-likevolume.

FIG. 10 is a schematic perspective view of completed second shell 23formed from preform 76, in accordance with an embodiment of theinvention. RF weld 110 has been completed with a sealing RF weld 112,thus completely sealing off the gas volume within the balloon-likevolume. In addition, the part of fill tube 86 outside the edge of secondshell preform 76 has been cut off.

In alternative embodiments, other methods, such as cementing, may beused instead of RF welding for attaching upper and lower sheets 80 and82 and upper and lower sheets 100 and 102 to each other.

Based on the inventors' experiments with a 250 mbar overpressure ofoxygen inside completed second shell 23, the leakage was found to be10⁻⁹ Torr-liter/second, yielding an estimated usable life-time exceeding10 years for completed second shell 23 inside a breast implant.Inflating completed second shell 23 with argon instead of air or oxygenmay reduce the leakage even further.

FIG. 11 is a schematic sectional view of PU/EVOH/PE composite material90 covering PA/PU composite material 70, in accordance with anembodiment of the invention. PU/EVOH/PE composite material 90 may becemented or otherwise attached to PA/PU composite material 70. Thethicknesses of the components of PA/PU composite material 70 (PA 72 andPU 74) in the figure, as well as those of the components of PU/EVOH/PEcomposite material 90 (PU 74, EVOH 92, and PE 94), are not to scale.Typical thicknesses of the components are 0.5-1.5 mm.

FIG. 12 is a schematic sectional view of PU/EVOH/PE composite material90 covering both sides of PA/PU composite material 70, in accordancewith an embodiment of the invention. PU/EVOH/PE composite material 90may be cemented or otherwise attached to one or both sides of PA/PUcomposite material 70, after which second shell 23 is assembled from theresulting material by RF welding. Second shell 23, which is fabricatedof material with PU/EVOH/PE composite material 90 on both sides of PA/PUcomposite material 70, is typically less flexible than a shellfabricated of material with a single sheet of PU/EVOH/PE compositematerial (as shown in FIG. 11).

FIGS. 13-15 show the construction of second shell 23 using agas-impermeable coating, in accordance with an embodiment of theinvention.

FIG. 13 is a schematic perspective view of coated second shell preform76, in accordance with another embodiment of the invention. Coatedsecond shell preform 76 is a result of depositing an impermeable coatingas an upper coating 122 and a lower coating 124 on both sides of secondshell preform 76 of FIG. 5.

In a first alternative embodiment of the coating, the depositioncomprises spraying graphene oxide in a water dispersion onto secondshell preform 76, and allowing it to dry. Graphene oxide in waterdispersion is available from Graphenea, Paseo Mikeletegi 83, 20009 SanSebastian, SPAIN.

In a second alternative embodiment, the deposition comprises sprayingaluminum oxide in a water dispersion onto second shell preform 76, andallowing it to dry. Aluminum oxide in water dispersion is availablefrom, for example, American Elements, 10884 Weyburn Avenue, Los Angeles,Calif. 90024, USA. In a third alternative embodiment, the depositioncomprises spraying titanium oxide in a water dispersion onto secondshell preform 76, and allowing it to dry. Titanium oxide in waterdispersion is available from, for example, US Research Nanomaterials,Inc., 3302 Twig Leaf Lane, Houston, Tex. 77084, USA.

For all three suspensions of graphene oxide, aluminum oxide, andtitanium oxide, more than one spray coating may be applied in order toattain sufficient impermeability. The spray coating is allowed to drybetween successive applications.

After drying, each of the three oxides forms gas impermeable upper andlower coatings 122 and 124, respectively. All three oxides used asalternative embodiments in the coating (graphene oxide, aluminum oxide,and titanium oxide) are fully biocompatible.

FIG. 14 is a schematic perspective view of second shell preform 76 afterthe preform has been inflated with air or other gas, in accordance withan embodiment of the invention. Upper composite sheet 80 with coating122 and lower composite sheet 82 with coating 124 have formed aballoon-like volume due to the inflation of second shell preform 76through fill tube 86.

FIG. 15 is a schematic perspective view of completed second shell 23formed from preform 76 of FIG. 14, in accordance with an embodiment ofthe invention. RF weld 90 has been completed with a sealing RF weld 126,thus completely sealing off the gas volume within the balloon-likevolume. In addition, the part of fill tube 86 outside the edge of secondshell preform 76 has been cut off.

FIG. 16 is a schematic sectional view of completed breast implant 21, inaccordance with an embodiment of the invention. Completed second shell23 (as described with reference to FIG. 10 or FIG. 15) has been insertedinto first shell 22 (FIG. 2) through opening 62. Second shell 23 isfurther secured in place by a ring of cement 130, which attaches thesecond shell to first shell 22. Cement 130 also closes off the inside offirst shell 22, thus enabling the subsequent filling of the first shellwithout leakage of the fill material, as will be described below.Instead of cement 130, other methods may be used for securing secondshell 23 to first shell 22. Elements 132, 133, 134, and 136 aredescribed further below.

Breast implant 21 is depicted in FIG. 16 as having the cross-sectionalshape of an oval. However, due to the flexibility of the material offirst shell 22 and completed second shell 23, as well as the elasticityof filler material 132, it will adapt its shape according to thesurrounding tissue as shown in FIG. 1.

FIG. 17 is a flowchart 230 that schematically illustrates a method forfabricating breast implant 21, in accordance with embodiments of theinvention. The method splits into two paths 234 and 236 from a startstep 232. Path 234 leads to a first shell fabricating step 238, whichcomprises the fabrication of first shell 22 by dip-casting as describedabove with reference to FIG. 2. Path 236 leads to steps 240-254 forfabricating second shell 23.

In a first material fabrication step 240 PA/PU composite material 70 forsecond shell 23 is fabricated as described above with reference to FIG.3. In a cut and weld step 242, two pieces 80 and 82 of compositematerial 70 are cut to shape and attached to each other to form secondshell preform 76 with fill tube 86 as described above with reference toFIGS. 4-5.

After first cut and weld step 242, the process splits into alternativeembodiments, with the first comprising steps 244-248 and the secondcomprising step 250.

In the first alternative embodiment, in a second material fabricationstep 244 PU/EVOH/PE composite material 90 is fabricated and cut tosheets 100 and 102 as described above with reference to FIGS. 6-7. Withreference to FIG. 8, in an EVOH cementing step 246, sheets 100 and 102are cemented to second shell preform 76 from first cut and weld step242. With further reference to FIG. 8, in a weld step 248 sheets 100 and102 are RF welded to each other.

In the second alternative embodiment, in a coat step 250 second shellpreform 76 from first cut and weld step 242 is coated by one of threeimpermeable coatings, as described above with reference to FIG. 13.

The alternative embodiments described above now converge and continue inan inflation step 252, where second shell preform 76 is inflated withgas as described above with reference to FIGS. 9 and 14. In a seal step254 inflated second shell preform 76 is sealed with an RF weld and filltube 86 is cut off as described above with reference to FIGS. 10 and 15.The result of seal step 254 is completed second shell 23.

Step 238 and steps 240-254 may be implemented serially or in parallel.These steps converge in a second shell insertion step 256, wherecompleted second shell 23 is inserted and secured in first shell 22 asdescribed above with reference to FIG. 16. Further referencing FIG. 16,in a cap step 258 a cap 136 of the same material as first shell 22 isused to close opening 62. The use of cap 136, in addition to cement 130,further secures implant 21 against leaks of elastic filler material 132.

In an implant fill step 260 first shell 22 is filled with an elasticfiller material 132 using a syringe (not shown) through a shell wall 133at a location 134, until a predetermined volume of material has beeninjected. After implant filling step 260, the silicone gel is set,typically at an elevated temperature of approximately 160° C.

After completing the injection of the material, the injection hole atlocation 134 is sealed in a seal step 262 using the same material asused for fabricating first shell 22. A typical volume of breast implant21 is 800 cc. Were second shell 23 not inserted into first shell 22, theentire 800 cc volume would be filled with elastic filler material 132,weighing approximately 800 g. The volume of the second shell istypically 30-40% of the total volume of breast implant 21, leading to areduction of the injected elastic filler material 132 by 30-40% of thevolume of 800 cc, which in turn reduces the weight of the implant by30-40% of the weight of 800 g.

Elastic filler material 132 typically comprises a 2-component siliconegel. The silicone gel is a viscose liquid while being injected throughthe syringe. Before the silicone gel is injected into first shell 22,air bubbles are removed from the gel under vacuum.

It will be appreciated that the embodiments described above are cited byway of example, and that the present invention is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present invention includes both combinations and subcombinationsof the various features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

1. (canceled)
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 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. A method for manufacturing an implantable device, themethod comprising: providing a first sealed flexible shell configuredfor implantation within a breast of a human subject; filling the firstsealed flexible shell with an elastic filler material; providing asecond sealed flexible, inelastic shell which is impermeable to a gas,such that an amount of the gas escaping from the second shell does notexceed 10−8 Torr-liter/second when the gas pressure inside the secondshell is 250 mbar higher than the gas pressure outside the second shell;disposing the second shell within the elastic filler material inside thefirst sealed flexible shell; and inflating the second shell with avolume of the gas; wherein the second sealed flexible, inelastic shellcomprises a first composite comprising polyamide and polyurethane, and asecond composite comprising polyurethane, ethylene vinyl alcohol andpolyethylene.
 13. (canceled)
 14. The method according to claim 12,wherein providing a second sealed flexible shell impermeable to a gascomprises depositing at least one coating impermeable to the gas on thesecond shell.
 15. The method according to claim 14, wherein the coatingcomprises graphene oxide, and wherein depositing the coating comprises:providing graphene oxide as a suspension in a liquid; applying theliquid on an outer surface of the second shell; and allowing the liquidto dry.
 16. The method according to claim 14, wherein the coatingcomprises aluminum oxide, and wherein depositing the coating comprises:providing aluminum oxide as a suspension in a liquid; applying theliquid on an outer surface of the second shell; and allowing the liquidto dry.
 17. The method according to claim 14, wherein the coatingcomprises titanium oxide, and wherein depositing the coating comprises:providing titanium oxide as a suspension in a liquid; applying theliquid on an outer surface of the second shell; and allowing the liquidto dry.
 18. The method according to claim 12, wherein filling the firstsealed flexible shell comprises filling the shell with silicone gel. 19.The method according to claim 12, wherein inflating the second sealedflexible shell comprises inflating the shell with air.
 20. The methodaccording to claim 12, wherein inflating the second sealed flexibleshell comprises inflating the shell with argon.